1. Field of the Invention
The invention relates to a method for estimating in real-time the parameters of a multi-phase induction machine.
2. Background Art
The use of induction machines in industrial applications in recent years is becoming more common, especially in automotive applications. An induction machine is particularly suited for an automotive environment because of its rugged nature and low cost. Examples of such applications include electric vehicles, hybrid electric vehicles in which an induction machine is a part of a powertrain that includes an internal combustion engine, fuel cell electric vehicles, integrated starter generator systems, electric power-assisted steering, etc. Induction machines for such applications provide potential for increased fuel economy and reduced engine exhaust emissions. They also make it possible to meet the demands of increased vehicle electrical loads.
An electric machine, when used in an automotive application, must be capable of operating with variable torque control over a fairly wide speed range. Controllers for such induction machines must rely upon known machine parameters.
The machine parameters in the case of control systems that do not rely upon sensors for measuring rotor position, speed or flux are estimated. In this way, control of the behavior of the induction machine in the powertrain is achieved as the operating conditions of the powertrain change and as the machine variables change.
Aside from the need for torque control, there is a need for estimating machine parameters for purposes of failure detection, analysis and failure mitigation. This requires an on-line estimation technique.
It is assumed for purposes of this invention disclosure that the invention is used to estimate the basic machine parameters of a machine that is part of a microcomputer-controlled, alternating current, drive system. The method of the invention is based on an induction machine model in a synchronously rotating frame. It utilizes sinusoidal pulse width modulated voltage signals in an identification test for the machine parameters. The microcomputer for the system includes an algorithm that provides an accurate estimation of the stator and rotor parameters based on stator current measurement and voltage commands. Torque measurements and position measurements are not required.
The method of the invention uses a parameter identification technique that includes projection of the stator voltage signal on the axes related with the stator current in a synchronously rotating frame.
The method of the invention includes the step of expressing stator voltage as a function of stator current, stator resistance, stator flux and stator excitation frequency. A functional relationship is established between rotor current, rotor flux, rotor resistance, electrical speed of applied stator voltage and rotor electrical speed. That functional relationship is transformed to eliminate derivatives and flux variables when an induction machine operates in a steady state condition. The rotor current is computed as a function of measured stator current. The stator voltage is calculated as a function of machine parameters; stator current, electrical speed and slip frequency.
The stator voltage components determine characteristic parameters, which are used to compute induction motor parameters.